1. Field of the Invention
The present invention relates to a semiconductor apparatus to which various different kinds of devices can be connected.
2. Description of the Related Art
1. A USB (Universal Serial Bus) port (interface) is mounted on various kinds of electronic devices such as cellular phones, PDAs (Personal Digital Assistants), laptop personal computers, etc. Various kinds of devices can be connected via a USB port. The electronic device judges whether a device is connected via the USB port, what kind of device is connected via the USB port, and the state of the device thus connected. Subsequently, the electronic device transits to an appropriate operation mode according to the judgment result. In many cases, various kinds of interfaces other than a USB port also must identify what kind of device is connected via a connector and identify the state of the connected device.
2. Furthermore, various kinds of electronic circuits such as CPUs (Central Processing Units) and DSPs (Digital Signal Processors) which are each configured to perform digital signal processing, liquid crystal panels, and other kinds of analog circuits and digital circuits, etc., are mounted on various kinds of electronic devices such as cellular phones, PDAs (Personal Digital Assistants), laptop personal computers, etc. With battery-driven electronic devices mounting a battery as a power supply, each electronic circuit included within the device operates using the battery voltage supplied by the battery.
Electronic devices are known having a function of receiving electrical power supplied from an external power supply via an AC adapter, USB (Universal Serial Bus) port, or the like. Such an arrangement enables operation to be performed even if the remaining battery charge becomes low, or even if a battery is not mounted on the electronic device. With such an arrangement, a power supply management circuit (power management IC) is provided, which performs a control operation for switching the voltage that is to be used to operate the electronic device between the voltage supplied from the external power supply and the voltage supplied from the battery. In a case in which the battery is a rechargeable battery such as a lithium-ion battery, the power supply management circuit has a function for charging the battery using the voltage supplied from the external power supply. The power supply management circuit makes a comparison between the voltage supplied from the external power supply and the battery voltage, and controls which of these voltages is to be supplied to a load, based upon the comparison result.